1. Field of the Invention
This invention relates to method and apparatus for preparing light-weight honeycomb mirrors, particularly by laser welding of the mirror components.
2. The Prior Art
The construction of large vitreous honeycomb mirrors is a well developed technology. Conventionally, honeycomb support structure is fabricated either by hand-welding individual ribs or by assembling short sections of square tubing; the latter being less time consuming. A large one-piece (e.g. 3' dia.) face plate is cut, ground and polished and mounted on the honeycomb structure. The bonding of the honeycomb structure to the face plate, is accomplished under pressure and at high temperature within a furnace.
Another method of construction uses devitrifying solder glass to join the honeycomb to the face plate. This glass-ceramic material converts under heat treatment to a crystalline structure having a CTE matching that of the material to be joined.
The major problem with these conventional methods is the high cost of labor involved. For example, the mirror blank for the Hubble space telescope cost in excess of $2,000,000. A mirror formed by the method of the present invention as discussed below, can be considerably cheaper.
Another problem associated with established techniques has been the size limitation imposed due to the scaleability of a one-piece face plate. The laser-welded mirror of the invention being an assembly of a plurality of face plates (or tiles) can be made smaller or larger as desired, as discussed below.
Also the flame of a hand-held welding torch can stray off the weld line, overheating portions of quartz plates and causing cracking thereof.
Representative of the prior art are U.S. Pat. No. 4,124,277 to Stang and U.S. Pat. No. 3,917,380 to Klein. Neither of these patents disclose laser welding of mirrors to honeycomb-ribs as a method of mirror formation.
There is need however to provide a light-weight honeycomb mirror to overcome the above prior art shortcomings.
There has now been discovered a method for making light-weight honeycomb mirrors that are of relatively low weight and high strength and which can be made with narrow weld lines and at reduced cost.